This invention relates to the preparation of hot asphalt or asphaltic concrete compositions and more particularly to the treatment of aggregate or aggregate plus asphalt with (1) water and (2) a sulfonic acid source selected from the group consisting of sulfuric spent acid and sulfuric acid sludge to provide an acidic asphaltic road paving composition having a pH less than 3.5 and preferably a pH less than 2. The treatment of the aggregate or the treatment of the aggregate plus asphalt with the sulfuric acid source and at least 1000 gallons of water per 100 tons of aggregate enables a reduction in the amount of asphalt from 10% to 40% while maintaining the required strength as measured by Marshall Stability and other tests.
The trend in the road building industry has gone from the use of liquid asphalts to using harder paving asphalts or asphaltic concretes which must be applied to an aggregate in a hot condition. This trend has been accelerated with the recent critical shortages of various fuels used as solvents to cut back the asphalts, such as gasoline, kerosene, diesel oil and fuel oil fractions. Another recent problem in the road building industry is the shortage and high cost of paving asphalts. The present invention enables the road builder to reduce the amount of asphalt by 10% to 40% while maintaining the required strength and wear resistance of prior art asphaltic compositions.
Common asphaltic compositions used for paving roads and used for the base material upon which the paving material is over-laid basically comprise a mixture of aggregate and asphalt. Typical aggregate formulations and asphalt properties are set forth in Standard Specifications, State of California Dept. of Public Works, Division of Highways, Jan. 1960, and in ASTM Standards on Bituminous Material for Highway Construction, Waterproofing, and Roofing, Ninth Edition, Oct. 1962. Enough asphalt is included so that complete coating of the aggregate particles is assured. The asphalt must coat the particles and cement the adjacent or adjoining particles together to achieve the required amount of strength necessary for a road construction material. The mixing of the aggregate and asphalt is generally done when the materials are hot to assure the proper coating and to make the mixture fluid enough to assure bonding after the composition is laid and rolled into a road surface on location.
When applying paving asphalts or asphaltic concrete, it is standard practice to heat both the asphalt and the aggregate to which it is to be applied. The asphalt is heated in order to increase its fluidity and flow characteristics so that it will thoroughly coat the aggregate and bond the adjacent particles together when it cools and hardens. The purpose for heating the aggregate is twofold. First, it is done so that the asphalt will not be chilled too rapidly when it comes in contact with the rock or gravel particles. This would prevent proper coating and cementing. Of equal or greater importance is the fact that any perceptible amount of moisture present upon the face of the aggregate will prevent coating to even a greater degree than the cooling or chilling effect of an unheated surface on the rock or stone. In order to maintain fluidity of the asphalt it has been maintained at a temperature of from 250.degree. to 300.degree. at the point of application. In order to thoroughly heat and dry the aggregate it has been subjected to a heating cycle at temperatures of from 275.degree. to 325.degree. for a period of time long enough to thoroughly dry the surface of the material. Since the amount of moisture present in aggregate stored outdoors will range from a low of 4% to as high as 12% by weight, the amount of heat required for the removal of the water stored in the aggregate mass is very high. If it is not removed, the finished product has been of poor quality.
In fact, this animosity towards water is displayed by all prior art asphalt compositions since water cannot be retained or "dissolved" therein. Although liquid asphalts, often referred to as "cutbacks," are sometimes applied at slightly elevated temperatures (100.degree. to 180.degree. F.), the aggregate to which they are applied is not heated. It is sometimes applied through a pugmill at or near a gravel pit or storage pile. However, it is most frequently added to the rock or gravel on the roadway itself along a windrow near the job site. If the aggregate is too wet at the time of the application, the asphalt may fail to "set up". When this happens it is usually necessary to rip or scarify the road and aerate it by blading or pulvamixing. Then it is laid down and compacted again. Sometimes when the work has been properly done a hard rainstorm occurring soon after the completion of the project will displace the asphalt to a lower depth in the base of the road or at times even wash it out into the ditches.
Emulsions which combine the asphalt, water, and detergents or wetting agents into a dispersion appear to solve some of the problems mentioned above. However, since high temperatures, a high volume of emulsifying agent (approximately 1% by weight), and a high energy input provided by powerful pumps and colloid mills is necessary for the production of these emulsions, they are quite expensive. In addition, they may not be used in materials that are excessively wet at the time of application and will frequently wash out after proper application during heavy precipitation. While these prior art asphalt compositions are classified as anionic, cationic or nonionic, they operate within a very narrow range centered upon a pH of 7 and their basic function is that of saponification.
There are other prior art compositions formulated for the purpose of generally improving the coating characteristics of asphalt and particularly directed toward overcoming the normally unsatisfactory wetting or coating action of unmodified asphalts in wet aggregates. Typical of such preparations are Dohse U.S. Pat. No. 2,191,295, Blott U.S. Pat. No. 2,603,573, Bransky U.S. Pat. No. 2,669,525, Wishlinski U.S. Pat. Nos. 2,675,328 and 2,705,681 and Brunel U.S. Pat. No. 3,470,006. All of these compositions utilize a wide variety of mineral and organic acids, filler materials, solvent mixtures, petroleum oils, phenols and neutralizing agents in order to produce waterproofing sealants, impregnating and anti-stripping agents which are blended with asphalt of heavy oils before incorporation into aggregate. All of them possess a pH at or above neutrality. Except for Blott, none of them claims that the application of the compound to the aggregate prior to the introduction of the asphalt is of benefit. While Blott permits the incorporation of various acids and phenol binders into the aggregate before neutralization, it is required that enough lime be present in the aggregate to bring the pH into the neutral zone.
These various preparations utilize an enormous variety of acidic materials. Mineral, naphthenic, carboxylic, hydroxy, lauric, myristic, palmitic, stearic, carnubic, oleic, linoleic, linolenic and various acid sludges are specified. To them are added various oils such as polymers, tall oil, unsaturated petroleum oils, alkyl aryl hydrocarbon oils, phenols and, at times, short and long chain alchols. Fillers such as chalk, asbestos and spent clay are usually incorporated. In every example, various carbonates or, preferably, hydrated or deydrated lime is used in order to neutralize the compound, thus creating a specialized saponified product, or at least, one that contains water-insoluble acid soaps or metal sulfonates.
It has long been known that the incorporation of lime directly into any asphalt is highly detrimental since it causes embrittlement and excessive oxidation, thus shortening its life. It has also been recognized that adding lime or any other hydroxide to the aggregate prior to blending in the asphalt, while not as deleterious as its incorporation into the asphalt, is still detrimental, or, at best, of little or no value. On the other hand, it has also long been known that the incorporation of acids, even in dilute solutions causes a premature disintegration of the resulting asphaltic composition. It is for these reasons that, until now, it has been considered necessary that all compounds utilized in conjunction with asphalt must be at or near neutrality.
The art as taught by Holmes in patent No. 2,469,728 appears to contradict the premise outlined above. However, it is to be noted that the aggregates specified are limited to calcareous materials such as oyster and clam shells which are notoriously difficult to coat with asphalt, both because of their high moisture-retention characteristics and high pH. Since a wide variety of mineral and organic acids are specified, it is obvious that neutralization of the surface of the aggregate was the primary object of the treatment since an asphalt containing an amine wetting agent is specified in conjunction with the process. This is further borne out by that fact that the strength of the dilutions recommended are from 2% to 10%, approximately 10 times the rate I specify. It is also obvious that the unique properties possessed by the sulfonic acids were not recognized since they are not mentioned.
By virtue of their neutrality none of the preparations described by Dohse, Blott, Bransky or Wishlinski are capable of reacting or interacting with the surface of the aggregate, whether they are blended into the asphalt prior to application to the aggregate or introduced into the aggregate before the asphalt is applied. In these patents and in scores of others that I have examined, it is obvious that the unusual catalytic and surfactant properties inherent in the sulfonic acids, especially those that are entirely or predominately watersoluble have not been known to the art. In some cases the wide variety of acids specified or suggested confirms this fact, the Blott patent being a case in point. When a potential sulfonic acid source is specified, as in the Bransky patent, the two Wishlinski patents and that of Brunel, it is the heavy, viscuous, low acid and, correspondingly, sludges sometimes referred to as "liver" that are relatively insoluble in water that are required. Their insolubility is further enhanced by the incorporation of additional aromatic hydrocarbons, aliphatic petroleum oils, phenols and catalytic cycle stocks. In every case it is the announced purpose of the invention to produce a "soap mixture" (Bransky, column 3, line 33, U.S. Pat. No. 2,669,525; Wishlinski "water-insoluble sludge acid soaps", column 1, line 25, U.S. Pat. No. 2,675,328; Wishlinski, "water insoluble soaps of sulfonic acids", column 1, line 33, U.S. Pat. No. 2,705,681, and Brunel, "to produce corresponding soaps which act as agglutinizing agents", column 1, line 70, U.S. Pat. No. 3,470,006). Even if those sources of sulfonic acid preferred in my invention, i.e., spent acids and sludges that are nonviscous and with acidities of from 60% to 92% and preferably from 82% to 87%, were substituted for the heavy sludges specified by these and many other patents, the inclusion of the oils, phenols, etc. and the neutralization of the composition to a narrow range centered upon pH 7 would completely destroy their usefulness for my purposes.
All of these prior art compositions of Holmes, Bransky, Blott, Dohse, Wishlinski and others were formulated for the purpose of obtaining the better adhesion of liquid asphalts, usually known as "cutbacks", to wet aggregates. They are of no value in the asphaltic materials used in hot mix plants because of the necessity for completely drying the aggregate before adding the asphalt and because the practice of applying relatively pure asphalt heated to high temperatures and applied to the surface of hot, dry aggregate had eliminated the need for such additives. Neither have any of the emulsions been found either beneficial or compatible with hot plant practice.
In accordance with the present invention, the copious use of water combined with the maintenance of an acid pH, preferably below 2.0, obtained exclusively by the use of dilute sulfonic acid-water solutions, differentiates the compositions of the present invention from the prior art compositions containing emulsifying agents, or anti-stripping agents that have long been used by the petroleum industry.
It is apparent that the accelerated reduction-oxidation reactions that occur immediately following the application of the acid-water solution are concentrated primarily at each site where some metal is present upon the face of the aggregate or soil particle in the silicon-oxygen structure that comprises approximately 75% of the bulk and volume of most rocks and soil materials. The metals most commonly found at sites of substitution for silicon in the structure of soils and rock are: aluminum 8.1%, iron 5.1%, calcium 3.6%, sodium 2.8%, potassium 2.6% and magnesium 2.1%. Many other micro elements are also found, but they are unimportant to the content of this patent. It appears obvious that the conversion of these various metals situated in the soil structure and exposed upon the surface, to metal sulfonates (aluminum sulfonate, iron sulfonate, calcium sulfonate, calcium sulfonate, etc) is, in a large measure, responsible for the increased compatability of asphalt with rock and soil particles and its tighter adhesion to them in contrast to the results achieved when they are converted to sulfates, nitrates or phosphates by the application of sulfuric, nitric or phosphoric acid, or, for that matter with any known organic acid.
The conclusion that the conversion of dilute sulfonic acid into the sulfonates of the various metals that are to be found exposed upon the surface of rock and soil particles and that the resultant coating possesses unique bonding qualities is supported by the fact that the reduction of the amount of asphalt required for satisfactory coating and cementation is still achieved even when it is applied after the aggregate has been thoroughly dried. That the sulfonate coating is thoroughly bonded is evidenced by the fact that the aggregate can be tumbled in a cylinder for long periods of time without deleterious effects upon the improved coating characteristics of the asphalt when applied subsequently. Neither is there any evidence of deterioration in the sulfonate coating upon long storage before reheating and applying the asphalt at a later date. Whether the bonds are semi-ionic or covalent, it is readily apparent that the conversion to sulfonates of the exposed sites where metals are present upon the face of the aggregate is vastly superior to attempting to first formulate such compounds and then to try to discover a way to cause them to become bonded to the aggregate afterwards. This is, in effect, what the other compounds such as emuslifying agents and anti stripping agents sought to achieve.
In addition to the presence of sulfonate deposits upon the surface of the aggregate as an aid to the coating of asphalt, properly selected sulfonic acid sources serve another important function. When a composition consisting of a dilute solution of sulfonic acid and water, aggregate and asphalt are agitated and heated, the asphalt is temporarily converted into an emulsion or a dispersion, thus greatly improving its fluidity and dispersibility and assuring better coatability and bonding of the aggregate. It is apparent that the emulsions or dispersions formed are of the so-called inverted type wherein the asphalt is the continuous phase and the solution is the discontinuous phase. This accounts for the unique properties displayed by such a composition that contains far more moisture than can usually be tolerated by hot asphaltic concrete, provided that the pH is maintained at a point below 3.5 and preferably below 2.0. Like any other emulsion, such a composition will dry out, or, to use the terminology usually applied to the phenomenon, it will "break", and the resulting paving will have all the properties of any other asphaltic concrete even though from 10% to 40% less asphalt is present.
It is possible to produce cationic inverted emulsions by introducing heated asphalt and sulfonic acid solution into a high speed blender or homogenizer such as the Barrington Mixer. However, such emulsions do not achieve the same results as the materials described in this specification because of the absence of the oxidation-reduction processes previously described and the absence of the sulfonate coating upon the aggregate. It is this unique dual chemical phenomenon that marks the novelty of the processes described in this patent. As a result, the hot plant operator may apply the asphalt after the aggregate is treated and dried, he can introduce asphalt and solution simultaneously or the solution and then the asphalt prior to or concurrent with heating or he can, if necessary, introduce the solution subsequent to heating and applying the asphalt. While, in theory, the best results are to be expected when the solution and then the asphalt are applied prior to heating, excellent results have been achieved using the other sequences described.
It has previously been thought necessary that such a hot mixture of aggregate and asphalt must be kept dry and heated to approximately 300.degree. F. to assure proper bonding on location. It has been found that by adding a dilute solution of sulfonic acid and water to aggregate or aggregate plus asphalt, the asphalt percentage can be reduced by 10% to 40% while maintaining the required bonding and strength.
The acid-water solution reacts with the aggregate to make it more receptive to asphalt coating so long as the aggregate-acid-water composition is at a pH less than 3.5 and preferably less than 2.0 so that the amount of water-acid solution brings the moisture content within a range of 4% to 12%, depending upon the gradation and absorption characteristics of the aggregate used.
It is an object of the present invention to provide an asphaltic composition having a reduced amount of asphalt while maintaining the required strength when laid and rolled into a road surface.
Another object of the present invention is to provide an asphaltic composition useful as a paving material and as a base material.
Another object of the present invention is to provide an asphaltic composition capable of providing porous paving material.
Another object of the present invention is to provide an asphaltic composition better adapted for producing hot paving emulsions prepared in a hot mix plant.
Another object of the present invention is in providing an asphaltic composition employing a sulfonic acid source.
Another object of the present invention is to provide an asphaltic composition containing enough water to assure proper fluidity and coatability of aggregate.
Another object of the present invention is to provide an asphaltic composition capable of being heated and laid down at location at a lower temperature.
Another object of the present invention is to provide a method of making an asphaltic composition employing the composition of the present invention in a hot mix plant.
Another object of the present invention is to provide an asphaltic composition capable of retaining heat for a longer period of time.
Another object of the present invention is to eliminate the need for incorporating additional petroleum-based softening agents, oils, hydrocarbons and asphalt when recycling asphalt reclaimed from existing streets and roadways in standard hot plants or specialized equipment such as the Mendenhall machines described in U.S. Pat. Nos. 3,845,941 and 4,000,000.
Another object of the present invention is to eliminate the need for the addition of petroleum-based softening agents, oils, hydrocarbons, asphalt and specialized rejuvenating agents such as Reclamite, produced by Witco Chemical Corporation's Golden Bear Division, when resurfacing or refinishing worn and oxidized asphalt wearing surfaces with heater planers, other standard road building and maintenance equipment and specialized equipment such as the Cutler machine.
Another object of this invention is to provide a means whereby standard roadbuilding and maintenance equipment supplemented by various means for supplying heat may be able to recycle all of the existing asphaltic surfacing in situ and thus dispense with the need for hauling it to a hot plant facility.
Another object of the present invention is to provide a means whereby standard equipment and supplemental sources of heat may be able to reuse all of the recycled asphalt as surfacing or, at the discretion of the engineer, apportion part of it for use as base material.